Method of and apparatus for measuring cross talk



1944. H. H. BENNING 2,355,776 5 METHOD OF AND APPARATUS FOR MEASURING CROSS-TALK Filed July 4. 1942 WEST ATTENDED STATION i 457 ATTENDED MOD s/amz. STAT/0N SOURCE APP 0/5 TURB/NG L/NE I I l I I0 PIZIOT M-00 AMO i AMP TERM sou/ac: APP

' /'CRO$STALK 29 2a /5- v /4 I 25 30 f & 1 7

2 v fi AMP DEMOO AMP MP ILOT DET SOURCE DISTURBED LINE 775w I 23 I 22 S /GNAL APP.

lNVENTOR H H BENN/NG ATTORNEY Patente d Aug. 15, 1944 UNITED STATES PATENT OFFICE METHOD OF AND APPARATUSFOR MEASURING CROSS. TALK.

Harvey H. Benning, LincolnP -ark, N. J assignor. to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporationof New York.

Application July 4, 1942, SerialNo. 449,819

'7 Claims.

conductors involved so that the cross-talk measurements would be accomplishedindependently of the maintenance of normal signal transmission. However, in certain carrier transmission systemsdeveloped recently and embodying a plurality of repeaters in the individual conductor pairs, it is not practical to interrupt normal signal transmission on both the'conductor pairs so that crosstalk'measurement had to be made during normal 1 ment'" for measuring cross-talk between two par- 1 allel. conductor pairs on. which normal signal.

transmission is taking place.

The object of the invention is to measure the cross-talk of two alternating. waves of identical frequency being simultaneously transmitted on two'parallel'con'ductor pairs.v

In carrier transmissionfsystems of recent development' asmentioned previously, the separate conductor pairs are arrangedfor opposite directions of transmission by embodying therein a plurality of one-Way repeaters such that at one terminal of each of the conductor. pairs is located suitable. signal transmitting apparatus together with a pilot'wave source while at the opposite terminal of each of'the conductor pairsis located an appropriate signal translating mechanism, As the ranges; of frequencies of the signal Waves transmitted on the individual conductor pairs are identical, thepilot waves individual to each.

conductor pair for regulating the gain characteristics of the repeaters therein are provided with corresponding individual frequencies. In a specific embodiment of the-present inVen-. tion, cross-talk measurements are .made at the frequencies of individual-pilot'waves.while normal signal transmission is being efiected on the two parallel conductor pairs. At one terminal of one conductor pair. the source of pilot waves havin a frequency hand a source of audiblewaves having a fixed. frequency f2 are applied to a modulating apparatus whose output, including a component having. afrequency equivalent to the frequency f1 and. upper and lower side-band components whose frequencies differ by the frequency ,fz-from thefrequency f1. ofthe pilot wave, is applied to the one terminal of the one. conductor pair. The component f1 serves to regulate the gain characteristic. of theindividual repeaters embodied in the one conductor pair. v

To the other conductor pair at a terminal corresponding to the opposite terminal of the one conductor pair is applied a source of a further pilot wave having the. frequency f1 while atthe opposite terminal of the other conductor pair is disposed a demodulating device for demodulating thepilot wave f1 individual to the other conductor pair and the upper and lower side-bandcomponents present therein as cross-talk. As a consequence, the output of the demodulating device is supplied to. an. amplifier-detector device arranged to select a componentjz whose frequency is equivalent to the frequency f2 of the modulating wave. The magnitude of the component f2 indicated on a suitable meter represents crosstalk at the frequency f1 from the one to the otherconductor pair. This procedure is repeated to measure cross-talk at the frequencies of the remaining pilot waves individual to the one pair and passing from the latter to the other pair.

The same procedure is employed to measure.

cross-talk at all frequencies of the pilot waves individual to the other pair and passing from the latter to the one pair. In the latter procedure the audible source and modulating apparatus are connected to the other pair while the demodulating and associated apparatus are connectedto theductor pair. lfllembodying spaced one-way amplifiers II and I2 arrangedfor WE signal trans- 2| located at the east attended station. At the latter station suitable signaling apparatus 22 connected to the E--W line l3 supplies thereto signal waves which are received by suitable signal translating terminal apparatus 23 located at the west terminal thereof. The broken lines indicate differing from the frequency ii of the pilot wave by an amount equivalent to the frequency f2 of the .audible wave. Thus, the modulator 26 transmits the modulation component whose frequency is equivalent to the frequency of the pilot wave f1 and which serves to regulate the gain characteristic of the WE amplifiers II and I2 in the well-known manner as previously pointed out. The modulation components comprising the upper and lower side-bands of the pilot wave ii are also transmitted on the WE conductor pairs i3. but do not materially interfere with the aforethat additional unattended stations may be interposed between the west and east attended stations. Signal transmission may be effected, for example, over a frequency range extending from audibility up to at least 4 megacycles. As both the conductor pairs I0 and I3 transmit identical frequency rangesof signal waves, the gain characteristics of the respective amplifiers II and I2 and I4 and I5 maybe regulated in the usual manner by identical, pluralities of pilot waves having corresponding individual frequencies. Depending on the frequency of the signal waves,'one or more pilot waves of individual frequencies may be simultaneously employed for such regulation. Thus, for example, the several pilot waves individual to each conductor pair may comprise frequencies of the order of 64, 556, 2064 and 3096 kilocycles. Hence, thepilot sources 24 and 25 located at the respective west and east attended stations will be understood to generate simultaneously and continuously the frequency at which cross-talk measurements are to be made for a purpose that will now be explained. v

1 In accordance with the present invention, the pilot-source at the west attended station is applied to a modulator 26 of a type to be explained subsequently and to which is also applied asource 21 of alternating wavesof fixed frequency. The output of the modulator 26 is supplied to the west terminal of the WE conductor pair I0. At the east terminal of the E.W conductor pair l3 the pilot source 25 is directly applied thereto. To the west terminal of the E-W conductor pair I3 is connected a demodulator 28 whose output is supplied to a selec-. tive amplifier-detector 29 which supplies its output to a meter 30. v In the .operation of the present invention, let it be assumed that cross-talk from the disturbing W -Econductor pair II] to the disturbed E-W conductor pair I3is to be measured at the frequency ii. In such case, the wave sources 24 and 25 located atthe respective west and east terminals of the conductor pairs I0 and I3 are understood to be generating simultaneously and continuouslypilotwaves having the frequency ii. The source '2! also located at the west terminal of the conductor pair I0 is generating a wave of the frequencyjz'which, for the purpose of this illustration, is assumed to be in the audible range. As the pilot wave f1 (from the source 24) and audible wave fziare simultaneously and continuo usly'applied to the modulator 26, the modulation components appearing in the output of the modulator 26 include a component having the frequency f1 and other components whose frequencies constitute the upper and lower sidebands of the pilot wave ii, that is, frequencies mentioned gain regulation of the WE amplifiers II and I2 by the component f1.

Portions of the upper and lower side-band components being transmitted on the disturbing WE conductor pair W are also transmitted as cross-talk to the disturbed E-W conductor pair I3 and are further transmitted thereon together with the pilot wave f1 supplied directly thereto by the source 25 as previously pointed out. Again, it is to be understood that while the pilot wave f1 .(from the source 25) serves to regulate the gain characteristic of the EW amplifiers I4 and I5, the cross-talk upper and lower side-band components being transmitted on the disturbed EW conductor pair I3 do not materially affect such regulation. The pilot wave ji (from the source 25) and the cross-talk upper and lower side-band components being transmitted on the E-W conductor pair I3 are supplied to the de-,

modulator 28. a

As a result of the demodulation action, the output of the demodulator 28 includes a component f2 whose frequencyis equivalent to the frequency f2 of the modulating audible wave supplied by the source 2'! to the modulator 26. The component f2 is selected bythe'amplifier-detector 29 which applies the detectedv wave to the meter 30,

the reading of which in response to the detected component f2 serves to indicate the magnitude of the cross-talk at the frequency f1. This procedure is repeated in like manner at the other individual frequencies of the pilot waves to measure the cross-talk thereat from the WE conductor pair ID to the EW conductor pair I3.

A similar procedure is employed to measure cross-talk from the EW conductor pair 13 to the WE conductor pair II) at all frequencies of the pilot waves individual to the EW conductor pair I3. In accordance with this procedure, the modulator 26 and audible wave source 21 are operatively associated with the pilot wave source 25 located at the east terminal of the EW conductor pair I 3, and the demodulator 28, amplifierdetector 29 and meter 30 are operatively connected to the east terminal of the W-eE conductor pair I0.

Obviously, the cross-talk measurements are not necessarily limited to pilot waves but may be also expeditiously accomplished at the frequency of any individual wave whose transmission cannot be interrupted without seriously impairing the fidelity of the transmission system.

What is claimed is:

l. The method of measuring cross-talk between two conductor pairs extending togetherand embodying one or more amplifiers in each thereof, which consists in continuously transmitting individual alternating waves of certain frequency on each of the two pairs at the same time for regulating a characteristic of the respective amplifiers, continuously transmitting also at the same time on one of the two pairs other alternata e Whose fr quencies differ from the certain frequency by a predetermined amount, deriving from said certain wave being'transmitted on the'othe'r of the two pairs and the portions of said other waves being transmitted on the other pair as cross-talk a component whose frequency is equivalent to the predetermined frequency difference betweensaid certain and other waves on the one pair, and observin cross-talk represented by' said component.

2. The method of measuring cross-talk between two conductor pairs extending together and embodying an amplifier in each thereof, which consists in generating an alternating wave having a certain frequency, translating said certain wave into one component whose frequency is equivalent to the certain frequency and other components whose frequencies differ from the certain frequency by a predetermined amount and continuously transmitting said one and other components on one of the pairs such that said one component controls the gain of the amplifier in the one pair, continuously transmitting on the other of the pairs at the same time a further alternating wave having the certain frequency for controlling the gain of the amplifier in the other pair, translating said further certain wave being transmitted on the other pair and the portions of said other components being transmitted thereon as cross-talk into a further component whose frequency is equivalent to the predetermined frequency difference between said one and other components on the one pair, and observing cross-talk represented by said further component.

3. The method of measuring cross-talk be- I tween two conductor pairs extending together and embodying an amplifier in each thereof, which consists in generating an alternating wave having a certain frequency, generating an alternating wave having a different frequency, translating said certain and different waves into upper and lower side-band components of said certain wave and another component whose frequency is equivalent to the certain frequency and continuously transmitting said side-band and other components on the first pair such that said other component controls the gain of the amplifier of the first pair, continuously transmitting at the same time a further alternating wave having the certain frequency on the second pair for controlling the gain of the amplifier therein, translating said further wave being transmitted on the second pair and the portions of said side-band components being transmitted thereon as cross-talk into a further component whose frequency is equivalent to the different frequency, and observing cross-talk represented by said further component.

4. In combination, two conductor pairs extending together and embodying an amplifier in each thereof, means to apply continuously to one terminal of the first pair a plurality of alternating waves including a wave having a certain fre--' quency and other waves whose frequencies differ by a predetermined amount from the certain frequency such that the certain wave controls a characteristic of the amplifier of the first pair, means to applycontinuously to the second pair at the same time at a terminal adjacent the opposite terminal of the first pair a further alternating wave of the certain frequency for controlling a characteristic of the amplifier of the second pair, means at the opposite terminal of the second pair to derive from the further wave being transmitted thereon and the portions of the other waves'being transmitted on the second pair as cross-talk ana'dditional wave'whose frequency is equivalent to thepredetermin'ed frequency difference between the certain" and other waves on the first pair, and means to observe cross-talk at the certain frequency as represented by the ad,- ditional wave,

5. In combination, two conductor pairs extending together and embodying an amplifier in each thereof, means at one terminal of the first pair to generate an alternating current having a certain frequency, means to translate said certain current into a plurality of components one of which has a frequency equivalent to the certain frequency and others of which have frequencies differeing from the certainfrequency by a predetermined amount and to apply continuously said one and other components to said one terminal of the first pair such that the one component regulates the gain characteristic of the amplifier of the first pair, means to apply continuously to the second pair at the same time at a terminal adjacent the opposite terminal of the first pair a further alternating current having the certain frequency for regulating the gain characteristic of the amplifier of the second pair, means connected to the opposite terminal of the second pair to translate the further current being transmitted thereon and the portions of the other components being transmitted thereon as cross-talk into a further component whose frequency is equivalent to the predetermined frequency difference, and means to observe crosstalk represented by the further component.

6. A system for measuring cross-talk between two conductor pairs extending together, comprising one or more amplifiers embodied in individual pairs such that a characteristic of said amplifiers is regulated by an alternating wave having a certain frequency, at one terminal of the first pair a source of alternating current of the certain frequency, a source of an alternating wave of a different frequency and means to translate both the certain and different waves into components of which certain ones comprise frequencies constituting the upper and lower side-bands of the certain wave and a further one whose frequency is equivalent the certain frequency and to apply continuously the side-band and further components to the one terminal of the first pair such that the further component regulates the characteristic of the amplifier of the first pair, a further source of an alternating wave having the certain frequency and applied continuously at the same time to the second pair at a terminal adjacent the opposite terminal of the first pair for regulating the characteristic of the amplifier of the second pair, means connected to the second pair at the terminal adjacent the one terminal at the first pair for translating the further certain wave being transmitted on the second pair and the upper and lower side-band components being transmitted thereon as cross-talk into an additional component whose frequency is equivalent to the frequency of the different wave, selective means to detect the additional component, and means responsive to the detected additional component for indicating cross-talk represented thereby.

'7. In combination, two conductor pairs extending together and embodying in each thereof an amplifier having a characteristic regulated by an alternating wave of certain frequency, means for continuously applying said certain wave to each of said pairs for regulating the characteristics of into a component whose frequency is equivalent to the predetermined frequency difference between said certain and other waves on said one pair, and means for observing the magnitude of said component as a measure of the magnitude of the cross-talk at said certain frequency, passing from said one to said other pair.

HARVEY H. BENNINGi 

